3461. Suzanne Simard: How Do Trees Collaborate?

By Suzanne Simard and Manoush Zomorodi, NPR, June 26, 2020

Suzanne Simard

MANOUSH ZOMORODI, HOST:

It's the TED Radio Hour from NPR. I'm Manoush Zomorodi. And for most kids around the country, school is officially out of session. But unlike other summers, many kids and teens are stuck at home because of the coronavirus pandemic. And so today, we've got an episode for everyone - kids, adults, parents, teens. You are all invited on this journey because we've invited a certain dad back on the show to share the coolest things he's learned over the years here on the TED Radio Hour, topics to blow the minds of young and old. And mystery guest host, can you please introduce yourself?

GUY RAZ, BYLINE: It's the TED Radio Hour from NPR. I'm Guy Raz. Hello, Manoush.

ZOMORODI: Yay. Hello, Guy. Welcome back.

RAZ: Thank you.

ZOMORODI: OK. So, Guy, not only were you the host of this show until you so graciously handed over the reins to me, but you are also the host of a rather popular podcast for kids, right?

RAZ: Yeah. It's called Wow In The World. It's a journey through real scientific research. And it sounds a little weird, but it's like a cartoon for the ear where me and my co-host, Mindy Thomas, go on journeys into space and back in time and underwater and everywhere in between searching for incredible scientific discoveries. And it's this joyful, wonderful experience for us and hopefully for the kids who listen to the show.

ZOMORODI: Well, that includes my kids. And we sort of figured, since you and I are both home with our children this summer, we thought, you know, you'd be the perfect person to come on and curate a special summer show for the entire TED Radio Hour family. And you have so kindly brought four of your favorite segments that you did over the years. How did you even begin to choose which segments you were going to bring to us?

RAZ: Well, I think, like you probably experience, Manoush, there are a lot of TED Talks that my kids love and are really inspired by. And then there's some that, you know, of course, are sort of over their heads, right?

ZOMORODI: (Laughter).

RAZ: But I really wanted to bring segments that spoke to curiosity and the sort of the awe that kids naturally have about the world, and so that's how we kind of came up with this collection.

ZOMORODI: And I will say I did feel that way about the first segment that you brought to us. This one is called, How Do Trees Collaborate? Tell us about it.

RAZ: I love this segment so much. So basically, scientists for - basically forever thought the trees competed against each other for resources - right? - for water and sun and nutrients. And, you know, they figured that the tallest trees in the forest were the strongest trees, right? It makes sense.

ZOMORODI: Right.

RAZ: But Suzanne Simard, the scientist that we're about to hear from, she totally changed the way that scientists now think about trees because it turns out they don't compete at all. In fact, trees collaborate. They work together through this mysterious underground superhighway.

ZOMORODI: There is an entire communication network happening under our feet. Let's listen.

(SOUNDBITE OF ARCHIVED NPR BROADCAST)

RAZ: Forest ecologist Suzanne Simard had a hunch.

SUZANNE SIMARD: Yes. That's right.

RAZ: She thought that trees could talk.

SIMARD: Just imagine, like, when you're walking through the forest, you might - you hear the crunching of the twigs under your feet and the rustling of the leaves.

(SOUNDBITE OF LEAVES RUSTLING)

RAZ: But she thought - what if there's more going on?

SIMARD: Like a big chattering going on that we can't hear, that they're attuned to each other.

RAZ: Now, at the time, a team of scientists in England were wrapping up an experiment.

RAZ: And the scientists took two of these pine seedlings, these baby trees, that were in the same box, in the same dirt, and then they exposed one of these seedlings to a radioactive carbon dioxide gas.

SIMARD: Carbon-14, a radioactive carbon.

RAZ: And what they found was that some of that radioactive gas, the carbon-14, made its way into the second seedling.

SIMARD: You could visualize it. You could see it.

RAZ: And so from this experiment, it seemed that somehow, these two plants in the same dirt were connected.

SIMARD: And I thought, wow, you know, maybe this is what's going on in my forest.

RAZ: Maybe, Suzanne Simard thought, maybe all the trees in a forest are connected in a kind of network.

SIMARD: You know, like our airport system, our transportation system, our social networks.

RAZ: And maybe, she thought, all of this was happening underground.

SIMARD: When we walk through the forest, what we see as human beings - we just see these, you know, beautiful trees growing out of the ground. But we don't see that they're actually completely linked underground in this superhighway.

RAZ: So Suzanne decided to prove this underground network existed. She devised an experiment using some of the same radioactive gas, a Geiger counter to measure it and a patch of birch and fir trees.

(SOUNDBITE OF TED TALK)

SIMARD: I figured the birch and the fir would be connected in a below-ground web.

RAZ: Suzanne picks up the story from the TED stage.

(SOUNDBITE OF TED TALK)

SIMARD: And I gathered my apparatus - plastic bags and duct tape and shade cloth, a paper suit, a respirator. And then I borrowed some high-tech stuff from my university. The first day of the experiment, we got out to our plot, and I pulled on my white paper suit. I put on my respirator. I put the plastic bags over my trees. I got my giant syringes, and I injected carbon-14, the radioactive gas, into the bag of birch.

I waited an hour. I figured it would take this long for the trees to suck up the CO2 through photosynthesis, send it down into their roots and maybe shuttle that carbon below ground to their neighbors. I went to my first bag with the birch. I pulled the bag off. I ran my Geiger counter over its leaves, (imitating Geiger counter). Perfect. The birch had taken up the radioactive gas. Then, the moment of truth. I went over to the fir tree. I pulled off its bag. I ran the Geiger counter up its needles. And I heard the most beautiful sound, (imitating Geiger counter).

(LAUGHTER)

SIMARD: It was the sound of birch talking to fir. And birch was saying, hey, can I help you? And fir was saying, yeah, can you send me some of your carbon? I was so excited.

(LAUGHTER)

SIMARD: I ran from plot to plot. And I checked all 80 replicates. The evidence was clear. paper birch and Douglas fir were in a lively two-way conversation. So it turns out the two species were interdependent, like yin and yang. And at that moment, everything came into focus for me. I knew I'd found something big, something that would change the way we look at how trees interact and for us, from not just competitors but to cooperators.

(SOUNDBITE OF MUSIC)

RAZ: Now, you have to understand that Suzanne's discovery was pretty revolutionary because up until this point, most ecologists believed that trees competed against each other, that their world was, like, a Darwinian struggle with winners and losers.

SIMARD: Yeah, you know, that they're competing for light and water and nutrients.

RAZ: And that the strongest trees were the ones that grew tall, the ones that dominated the canopy and took all the resources. But Suzanne's experiment showed that something else was true.

SIMARD: They're actually sending messages back-and-forth that balances the resource distribution among the community.

RAZ: In other words, trees aren't just connected. They're actually sharing resources with each other.

SIMARD: So what we found initially, if one tree had a lot of water in it or a lot of nitrogen or had high photosynthetic rate and if one tree is sick, then the neighboring tree shuttles more of those nutrients to that suffering tree.

RAZ: And when you say communicate, do they actually communicate? Like, do they warn each other about, like, a fire or an invasive species or something?

SIMARD: Yes. So if one tree gets damaged by, say, mountain pine beetle, the injured seedling will up its defense enzymes. And then the receiving tree will then increase its defense enzymes because it knows now that there is some kind of damaging agent around.

RAZ: Wow. So how are they doing this? Like, how are they communicating through an underground network?

SIMARD: So they're physically connected by these microscopic fungi. And...

RAZ: So mushrooms?

SIMARD: Yes, you're right. We call them hyphae or mycelium. In fact, like, if you were to, you know, peel back the surface of the forest floor, you'll see the fungi that are linking these trees together. They're very visible. And it's these white and yellow, different colored threads that are - they look like, you know, sewing threads. But they're fungal threads. And they're crisscrossed and going off in multiple directions. And they work together to create a very, you know, a very complex web. And they're in constant communication between all the trees.

(SOUNDBITE OF TED TALK)

SIMARD: Forests aren't simply collections of trees. They're complex systems with hubs and networks that overlap and connect trees and allow them to communicate, and they provide avenues for feedbacks and adaptation. And this makes the forest resilience. That's because there are many hub trees and many overlapping networks, but they're also vulnerable because hub trees are not unlike rivets in an airplane. You can take out one or two, and the plane still flies. But you take out one too many or maybe that one holding on the wings, and the whole system collapses. Well, you know, the great thing about forests as complex systems is they have enormous capacity to self-heal.

In our recent experiments, we found with retention of hub trees and regeneration to have diversity of species and genes and genotypes, that these mycorrhizal networks, they recover really rapidly. We need to regenerate our forests with a diversity of species and genotypes and structures by planting and allowing natural regeneration. We have to give Mother Nature the tools she needs to use her intelligence to self-heal, and we need to remember that forests aren't just a bunch of trees competing with each other. They're super cooperators. Thank you.

(APPLAUSE)

ZOMORODI: Oh, so good, Guy. Do you think about this segment, like, every time (laughter) you go for a walk...

RAZ: Yeah.

ZOMORODI: ...Through a forest, I'm guessing?

RAZ: Yeah. Yeah. I - all the time. I live in California, in Northern California. And every time I'm in a redwood forest, I think about Suzanne Simard and how trees and forests are models for us, for human beings.

ZOMORODI: In terms of the resiliency that they can help build in groups. I mean, I feel...

RAZ: Yeah.

ZOMORODI: ...Like this idea of helping each other, having that cooperation in our roots is actually really, really wonderful to think about in light of what's been going on in the world right now and...

RAZ: Yeah.

ZOMORODI: ...How much we need our neighborhoods and our communities to be resilient and help each other.

RAZ: Yeah. I mean, we will all, at some point in our lives, need help. And we can all also help. It's an incredibly simple idea, but it's also so powerful. And Suzanne's research just puts it out into the world in such a beautiful way.

(SOUNDBITE OF MUSIC)

ZOMORODI: OK. When we come back, Guy, we're going to go from the forest to the Caribbean Sea and some dolphins who actually have some things to say and communicate. You want...

RAZ: All right.

ZOMORODI: ...To make some clicking dolphin noises for me here?

RAZ: (Imitating dolphin).

ZOMORODI: I'm Manoush Zomorodi. And you're listening to the TED Radio Hour from NPR. Stay with us.

RAZ: (Imitating dolphin).

1378. Salamander: A Small Amphibian That Makes a Big Difference

By Richard Cuniff, The New York Times, April 7, 2014

Spotted Salamander

If someone asked you to name the top predator in North American forests, you might think of bears, or maybe great horned owls. But here’s another answer to think about: woodland salamanders.

These skittish, slippery amphibians literally live under a rock, or a log, or any convenient dark and damp forest habitat. As apex predators go, they are mainly small, a few inches long and weighing well under an ounce.

But they are hugely abundant — and very hungry. On an average day, a salamander eats 20 ants of all sizes, two fly or beetle larvae, one adult beetle and half of an insect called the springtail. And in doing so, they collectively affect the entire course of life in the forest — and perhaps far beyond.

According to a new study in the journal Ecosphere, salamanders play a significant role in the global carbon cycle. If flatulent cattle are among the black hats of climate change (the livestock industry emits 14.5 percent of human-associated greenhouse gases), then salamanders may just be the white hats, helping to stave off climate disaster. If no one has noticed this before, well, this is how it goes when you live under a rock.

The study — by Hartwell H. Welsh Jr., a herpetologist at the United States Forest Service’s research station in Arcata, Calif., and Michael L. Best, now at the College of the Redwoods in Eureka, Calif. — notes that salamanders’ prey consists almost entirely of “shredding invertebrates,” bugs that spend their lives ripping leaves to little bits and eating them.

Leaf litter from deciduous trees is on average 47.5 percent carbon, which tends to be released into the atmosphere, along with methane, when the shredding invertebrates shred and eat them.

If there aren’t as many shredders at work and the leaves remain in place, uneaten, they are covered by other leaves, “like being trapped under a wet blanket,” as Dr. Welsh put it. The anaerobic environment under those layers preserves the carbon until it can be captured by the soil, a process called humification.

At least in theory, having more salamanders in a forest should mean fewer shredding invertebrates and more carbon safely locked underground. The researchers tested this theory in a forest in northwestern California, laying out a series of 16-square-foot enclosures, like containers for raised-bed gardens.

Some of the enclosures had salamanders, others didn’t. Each enclosure was joined to its neighbors by low, screened openings, so invertebrates could move freely back and forth, but the salamanders had to remain in their enclosures.

The presence of salamanders resulted in a significant decrease in shredders: fly and beetle larvae, adult beetles and springtails. In the plots with no salamanders there were more shredders, and they consumed about 13 percent more of the leaf litter. Almost half of that lost weight was carbon, released into the atmosphere.

“It’s more than just a curious phenomenon,” Dr. Welsh said. “It’s real.”

The authors calculate that woodland salamanders at the density in their study would send 179 pounds of carbon per acre of forest down into the soil, rather than up into the atmosphere. Extrapolated to the huge numbers of woodland salamanders and other predators working in the leaf litter of forests around the world, that is enough to affect global climate.

Another factor is that many salamanders have no lungs. About 70 percent of all salamanders belong to a single family, the Plethodontidae, which in effect breathe through their skin. (A pulsing flap of skin under their throats, called the gular fold, lets in just enough air for a sense of smell.)

The process requires much less energy than breathing with lungs, enabling salamanders to “be really small and exploit really tiny things that are not calorically sufficient for birds or mammals,” said John C. Maerz, a salamander specialist at the University of Georgia who was not involved in the Ecosphere study. While humans, with their relentless metabolism, burn off most of what they eat, salamanders store large amounts of carbon, nitrogen and other nutrients in their own bodies, or in the form of abundant offspring.

This low-key lifestyle makes them the hidden masters of the forest — “the vacuum cleaners of the forest floor,” as Dr. Maerz put it.

But he and the Ecosphere authors do not entirely agree about what that means for the larger significance of salamanders.

Dr. Maerz thinks the effect on the carbon cycle may apply in wet conditions, but not when the weather is too dry for humification. He also worries about trying to apply what happens “in these little square meters” on a larger scale.

His own studies have demonstrated that stable isotopes of carbon and nitrogen in leaves end up, via shredding invertebrates, stored away in the flesh of salamanders — like “a standing crop of nutrients,” he said. But climate heroes? Dr. Maerz prefers to think of them simply as a dominant driver of the forest energy cycle.

Shahid Naeem, an ecologist and climate scientist at Columbia University, agreed that “temperature, rain and other nonbiological factors probably explain more about the carbon cycle than salamanders.”

But he added:  “What’s nice about the study is the elegant quantification of how a change in a food web has consequences — something a lot of people know when it comes to the big, visible species, but not when it comes to the smaller, less visible, ones.  Lose the salamanders, and there are effects that ripple through the system.”

The notion of losing something as abundant as salamanders is not all that far-fetched. Another new study, in the journal Global Change Biology, compares present-day salamanders with some of the 180,000 specimens collected across the United States by the herpetologist Richard Highton, now retired from the University of Maryland. Dr. Highton, who began collecting in 1957, thought he saw a decrease in salamander size and abundance beginning about 1980.

When Karen R. Lips, an amphibian specialist, came to the University of Maryland a few years ago, she decided to follow up that hunch. She and colleagues revisited many of Dr. Highton’s research sites, concentrating on relatively unchanged habitat in national parks and forests from Tennessee to Maryland. Their results showed that salamanders had shrunk in size by 8 percent in 55 years — about 1 percent per generation.

That is “one of the largest and fastest rates of change ever recorded in any animal,” Dr. Lips said. Worse, salamanders were disappearing; even the abundant and widely distributed red-backed salamander was often absent.

Dr. Lips, who had done pioneering research on the chytrid fungus pandemic devastating frog species, thought at first that it might be spreading to salamanders. But her team found almost no trace of chytrid in the salamanders they collected, nor could they attribute the changes to logging, acid rain or overcollecting by biologists.

Instead, the study concludes that salamanders, which were mostly small to start with, are becoming even smaller as a way to adapt to warmer weather and reduced rainfall. If so, they may well rank as both heroes and victims in the fight against climate change — with unknown consequences for the fate of the forests themselves.